engleski

Nano Structure of In-homogeneous Amorphous-nano-crystalline Si Thin Films by Grazing Incidence X-ray Diffraction

Amorphous-nano-crystalline silicon thin films consist of nanometer-sized crystalline silicon grains embedded in amorphous silicon matrix. Such structure, with nano-sized ordered domains exhibit quantum size effects that can be used in third generation of solar cells. The a-nc-Si: H samples 100-500 nm thick were deposited by Plasma Enhanced Chemical Vapor Deposition using mixture of silane and hydrogen as working gas under various deposition conditions. The structure of a-nc-Si:H was examined by Grazing Incidence X-ray Diffraction (GIXRD) using 8 keV X-ray beam (MCX beam line at synchrotron Elettra in Italy). The scattered intensity was obtained for several values of angle of incidence that were gradually increased starting from critical angle (total external reflection), in order to probe samples at different depth below the sample surface. From diffraction patterns, analyzed using Rietveld refinement, were estimated size distribution of nano-crystals, strain and crystalline/amorphous phase volume fraction as a function of distance from the surface, with 10-20 nm resolution. The mean values of nano-crystals size distributions were from several nm up to 10 nm. The crystals were smaller closer to substrate or equal sizes across the whole sample, depending on details of preparation. These structural properties were compared with the results obtained by High-Resolution Transmission Electron microscopy and optical properties in the range relevant for photovoltaic conversion. The accuracy of applied approach in structural analysis and possible application were discussed.

Nano Structure; Amorphous-nano-crystalline Si; Thin Films;; Grazing Incidence X-ray Diffraction

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